The invention relates to a process for the preparation of polyoxyalkylene glycols by catalytic reaction of H-functional initiators with lower alkylene oxides.
Polyoxyalkylene glycols are used in large amounts for the preparation of polyurethanes. They are usually prepared by catalytic addition of lower alkylene oxides, in particular ethylene oxide and propylene oxide, to H-functional polymerization initiators. The catalysts used are mostly alkali metal hydroxides or salts, of which potassium hydroxide is of greatest industrial significance.
In the synthesis of polyoxyalkylene glycols having long chains and hydroxyl values of from ca 26 to ca 60 mg of KOH/g, such as are used, in particular, for the preparation of flexible polyurethane foams, chain growth is accompanied by side reactions which cause irregularities in the chain structure. These by-products are referred to as unsaturated components and lead to impairment of the properties of the resulting polyurethane materials. In particular, such unsaturated components exhibiting an OH functionality of 1, give rise to the following:
by reason of their low, in some cases very low, molecular weight, they are volatile and thus increase the total content of volatile matter in the polyoxyalkylene glycol and in the polyurethanes, in particular flexible polyurethane foams, prepared therefrom;
they act as chain stoppers during production of polyurethane, because they slow down or reduce the cross-linkage of polyurethane or the build-up of molecular weight of polyurethane;
they reduce the effective OH functionality of the synthesized polyoxyalkylene glycols; thus commercial polyether polyalcohols used for flexible foams and initiated with glycerol and catalyzed with potassium hydroxide have an effective OH functionality of only approximately 2.1 to 2.6, although the glycerol used is a trifunctional polymerization initiator.
It is therefore industrially very desirable to avoid unsaturated components as far as possible. On the other hand, many, in some cases complex, polyurethane formulations are set to accommodate polyoxyalkylene glycols having OH functionalities of from 2.1 to 2.6. It is therefore desirable to prepare polyoxyalkylene glycols having OH functionalities of from 2.1 to 2.6 but having only a minimum of unsaturated components.
Hitherto there has been no lack of attempts to provide polyoxyalkylene glycols having a low content of unsaturated components. Attempts to achieve this end particularly involve changing the alkoxylation catalysts used. Thus EP-A 268,922 proposes the use of caesium hydroxide. This makes it possible to lower the concentration of unsaturated portions, but caesium hydroxide is expensive and difficult to dispose of.
Furthermore, it is known to use multimetal cyanide catalysts, mainly zinc hexacyanometallates, for the preparation of polyoxyalkylene glycols having low contents of unsaturated components. A great many documents describe the preparation of such compounds. Thus DD-A 203,735 and DD-A 203,734 describe the preparation of polyoxyalkylene glycols using zinc hexacyanocobaltate. By using multimetal cyanide catalysts it is possible to lower the content of unsaturated components in the polyoxyalkylene glycol to from ca 0.003 to 0.009 meq/g; in the case of conventional catalysis using potassium hydroxide approximately 10 times this amount (from ca 0.03 to 0.08 meq/g) is found.
In addition, the preparation of zinc hexacyanometallates is known. Usually the preparation of these catalysts is carried out by causing solutions of metal salts, such as zinc chloride, to react with solutions of alkali metal or alkaline earth metal cyanometallates, such as potassium hexacyanocobaltate. To the resulting suspension of precipitated matter there is usually added, immediately after the precipitation process, a water-miscible component containing heteroatoms. This component may be present in one or both of the educt solutions. This water-miscible component containing heteroatoms can be, for example, an ether, a polyether, an alcohol, a ketone or a mixture thereof. Such processes are described for example in U.S. Pat. No. 3,278,457, U.S. Pat. No. 3,278,458, U.S. Pat. No. 3,278,459, U.S. Pat. No. 3,427,256, U.S. Pat. No. 3,427,334, U.S. Pat. No. 3,404,109, U.S. Pat. No. 3,829,505, U.S. Pat. No. 3,941,849, EP 283,148, EP 385,619, EP 654,302, EP 659,798, EP 665,254, EP 743,093, EP 755,716, U.S. Pat. No. 4,843,054, U.S. Pat. No. 4,877,906, U.S. Pat. No. 5,158,922, U.S. Pat. No. 5,426,081, U.S. Pat. No. 5,470,813, U.S. Pat. No. 5,482,908, U.S. Pat. No. 5,498,583, U.S. Pat. No. 5,523,386, U.S. Pat. No. 5,525,565, U.S. Pat. No. 5,545,601, JP 7,308,583, JP 6,248,068, JP 4,351,632 and U.S. Pat. No. 5,545,601.
DD-A 148,957 describes the preparation of zinc hexacyanoiridate and the use thereof as catalyst for polyether polyalcohol synthesis. Hexacyanoiridic acid is used as starting material. This acid is isolated as a solid and used in this form.
EP-A 862,947 describes the preparation of other double-metal cyanide complexes, in particular the use of cyanocobaltic acid or an aqueous solution thereof, as educt. The double-metal cyanides produced according to the teaching of EP-A 862,947 show high reactivity for ring-opening polymerization of alkylene oxides.
Multimetal cyanide catalysts show extremely high polymerization rates and make it possible to achieve high space-time polymerization yields. However, the use of multimetal cyanide catalysts involves considerable restrictions as regards the H-functional polymerization initiators that can be used. There are two types of initiators.
Some polymerization initiators are suitable for the so-called batch initiating method. These polymerization initiators, referred to below as batch starters, are placed in the reactor as the initial component of the batch and are freed from oxygen by repeated nitrogen purges and de-watered in vacuo at xe2x89xa61 mbar over a period of from 30 to 120 min at from 50xc2x0 to 120xc2x0 C., the de-watering time and de-watering temperature depending on the boiling point of the batch starter. The multimetal cyanide catalyst is then added and the nitrogen purge and de-watering are repeated, if necessary. Following the addition of the alkylene oxide, compounds that are suitable for use as batch starters cause, at reactor temperatures of from 90xc2x0 to 140xc2x0 C., commencement of the polymerization reaction, noticeable from a pressure drop in the reactor, after a time lapse of from a few minutes to, at most, 2 hours. If the reaction does not start within a period of 2 hours, the polymerization initiator is not suitable for use as a batch starter.
In practice it is found that the following polymerization initiators are especially suitable for use as batch starters: castor oil and fatty alcohols such as 1-dodecanol. However, polyetherols primed with fatty alcohols are unsuitable for the preparation of flexible PU foam. Castor oil is theoretically suitable for use as a polymerization initiator for polyetherols for the production of flexible foams, but it is not available in sufficient quantities or at consistent quality. Batch starters of particular significance are ethoxylates and propoxylates having molar masses xe2x89xa6400 dalton. These polymerization initiators usually have to be prepared by alkoxylation of low-molecular initiators, such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, in particular glycerol and trimethylol propane, with alkaline catalysts such as KOH. Before these polymerization initiators can be used for polymerization using the multimetal cyanide catalysts, the alkaline catalyst must be removed quantitatively, which is economically disadvantageous.
When use is made of tripropylene glycol as the initiator it has been found that it itself and its alkoxylates having molar masses below 400 dalton are suitable for use as batch starters. However tripropylene glycol and its alkoxylates having molar masses of less than 400 dalton show less advantageous starting characteristics than eg a linear polypropylene glycol having a number-average molar mass of 400 dalton.
A considerable drawback of the processes of the prior art is the fact that a polymerization initiator that is so significant in industry, such as glycerol, and which is used as starter for most of the commercial polyols used in applications involving flexible polyurethane foams, is not suitable for use as a batch starter for the reason that the reaction does not start. Glycerol can indeed be added to a suitable batch starter in a concentration of 10 wt % or 20 wt % without hindering the start-up of the reaction, but this does not adequately overcome the aforementioned economical drawbacks.
Glycerol is suitable for the so-called addition method, however, as U.S. Pat. No. 5,777,177 discloses. In the addition method, the alkoxylation reaction is primed with a batch starter and, when the reaction has reached a steady state, there is added another polymerization initiator, such as glycerol, along with the alkylene oxides, in a quantity which is sufficiently small not to cause the reaction to stop. In order to achieve a sufficiently narrow molar-mass distribution of the polyetherol, the addition of the glycerol is completed well before the addition of the alkylene oxide.
Polymerization initiators which are not suitable for use as batch starters but can be used in the addition method are referred to below as addition initiators. Examples thereof are glycerol, propylene glycol and ethylene glycol.
However, the addition method requires changes to be made to the existing production plants so that it may be desirable to use only batch starters and nevertheless utilize all of the advantages of multimetal cyanide catalysis.
It is an object of the present invention to provide polymerization initiators which are suitable for use as batch starters and which make it possible to achieve high space-time yields of polyetherols using multimetal cyanide catalysts.
Surprisingly, it has been possible to achieve this aim by the use of butane-1,4-diol, xcex1-hydroxy-xcfx89-hydroxypoly(oxybutane-1,4-diyl), pentane-1,5-diol, decane-1,10-diol or mixtures of at least two of these compounds. Homologues such as propane-1,3-diol and hexane-1,6-diol were found to be unsuitable for use as batch starters, since the alkoxylation reaction did not start within a period of 2 hours under otherwise identical conditions. The compounds xcex1-hydroxy-xcfx89-hydroxypoly(oxybutane-1,4-diyl) belong to a class of materials comprising oligomers and polymers of butane-1,4-diol, which can be prepared, for example, by the catalytic addition of tetrahydrofuran to butane-1,4-diol.
Accordingly, the invention relates to a process for the preparation of polyether polyols by catalytic reaction of H-functional initiators with lower alkylene oxides, wherein multimetal cyanide compounds are used as catalysts and butane-1,4-diol, xcex1-hydroxy-xcfx89-hydroxypoly(oxybutane-1,4-diyl), pentane-1,5-diol, decane-1,10-diol or mixtures of at least two of these compounds are used as H-functional initiators.
The invention also relates to the polyether alcohols produced by the process of the invention, to their use for the preparation of polyurethanes and to the polyurethanes manufactured therefrom.
Preference is particularly given to the use of butane-1,4-diol, xcex1-hydroxy-xcfx89-hydroxypoly(oxybutane-1,4-diyl) and pentane-1,5-diol as initiators. When these compounds are used as the initiators for the process of the invention the time lapse prior to start-up of the reaction is particularly short, so that the space-time , yield is particularly high. The molecular weight of xcex1-hydroxy-xcfx89-hydroxypoly(oxybutane-1,4-diyl) preferably ranges from 200 to 2500 g/mol.
In a preferred embodiment of the invention, the polymerization initiators employed in the process of the invention are used together with other H-functional initiators.
Due to this possibility of also using known, in particular trifunctional, initiators such as glycerol or trimethylol propane, the process of the invention can also produce polyether alcohols having a functionality ranging from 2.1 to 2.6, as commonly used for the preparation of flexible polyurethane foams. The quantity of the additional polymerization initiators used should be such that the final products exhibit the desired functionality, but should not exceed 10%, based on the polymerization initiator used, since it could then result in delayed start-up of the reaction. In one embodiment of the process of the invention, the polymerization initiators that are additionally used are reaction products of the said polymerization initiators with alkylene oxides. These reaction products preferably have a molecular weight in the range of from 300 to 600.
Alternatively, the known addition initiators, such as glycerol, can be metered to the reaction system following initiation of chemical addition of the alkylene oxides to the polymerization initiators used in the process of the invention. In this case the addition initiators can be introduced in a concentration of up to 200 mol %, based on the batch starter used. It is thus possible to prepare polyetherols having a functionality of up to 2.66.
The multimetal cyanide compounds used for the preparation of polyetherols of the invention are known to be very active catalysts for the preparation of polyfunctional polyethers.
Details on the synthesis and usage of these multimetal cyanide complexes for the preparation of polyfunctional polyethers are disclosed in the following documents:
U.S. Pat. No. 3,278,457, U.S. Pat. No. 3,278,458 and U.S. Pat. No. 3,278,459, U.S. Pat. No. 3,427,256, U.S. Pat. No. 3,427,334, U.S. Pat. No. 3,404,109, U.S. Pat. No. 3,829,505, U.S. Pat. No. 3,941,849, EP 654.302 and U.S. Pat. No. 5,470,813, EP 743,093, WO 97/23,544, WO 97/26,080, WO 97/29,146, WO 97/40,086, U.S. Pat. No. 5,714,428, U.S. Pat. No. 5,593,584, U.S. Pat. No. 5,527,880, U.S. Pat. No. 5,482,908.
Preparation of the multimetal cyanide compounds can be effected using the manufacturing processes disclosed in said specifications.
These manufacturing processes usually comprise the following process steps:
a) adding an aqueous solution of a water-soluble metal salt of the general formula
M1m(X)n,
xe2x80x83in which
M1 is at least one metal ion selected from the group comprising Zn2+, Fe2+, Co3+, Ni2+, Mn2+, Co2+, Sn2+, Pb2+, Fe3+, Mo4+, Mo6+, Al3+, V5+, Sr2+, W4+, W6+, Cu2+, Cr2+, Cr3+, Cd2+,
X is at least one anion selected from the group comprising halide, hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate and carboxylate, in particular formate, acetate, propionate, oxalate, nitrate, and
m and n are integers which correspond to the valences of M1 and X,
to an aqueous solution of a cyanometallate compound of the general formula
HaM2(CN)b(A)c,
xe2x80x83in which
M2 denotes at least one metal ion selected from the group comprising Fe2+, Fe3+, Co3+, Cr3+, Mn2+, Mn3+, Rh3+, Ru2+, Ru3+, V4+, V5+, Co2+, Ir3+and Cr2+ and
M2 can be the same as or different from M1,
H denotes hydrogen or a metal ion, usually an alkali metal, alkaline earth metal or ammonium ion,
A denotes at least one anion selected from the group comprising halide, hydroxide, sulfate, carbonate, ROC=N, thiocyanate, isocyanate, carboxylate or nitrate, in particular cyanide, and A can be the same as or different from X and
a, b and c are integers which are selected such that electroneutrality of the cyanide compound is achieved,
one or both of the solutions optionally containing at least one water-miscible ligand containing heteroatoms, which is selected from the group comprising alcohols, aldehydes, ketones, ethers, polyethers, esters, ureas, amides, nitriles, sulfides or functionalized polymers as described in U.S. Pat. No. 5,714,428,
b) combining the aqueous suspension that is formed in step a) with a water-miscible ligand containing heteroatoms, which is selected from the above group and which may be the same as or different from the ligand of step a), and
c) optionally separating the multimetal cyanide compound from the suspension.
In the syntheses of the multimetal cyanide compounds it is advantageous to use the acid as cyanometallate compound, since this avoids the otherwise inevitable formation of a salt as by-product.
These usable cyanometallate hydracids are stable in aqueous solution and have good handling properties. Preparation thereof can be carried out, for example as described in W. Klemm, W. Brandt, R. Hoppe, Z. Anorg. Allg. Chem. 308, 179 (1961), starting from the alkali metal cyanometallate to give, via the silver cyanometallate, the cyanometallate hydracid. Another possibility is to convert an alkali metal cyanometallate or alkaline earth metal cyanometallate by means of an acid ion exchanger to a cyanometallate hydracid, as described in F. Hein, H. Lilie, Z. Anorg. Allg. Chem. 270, 45 (1952), or A. Ludi, H. U. Guedel, V. Dvorak, Helv. Chim. Acta 50, 2035 (1967). Other methods of synthesizing the cyanometallate hydracids are given, for example, in xe2x80x9cHandbuch der Praeparativen Anorganischen Chemiexe2x80x9d, G. Bauer (Editor), Ferdinand Enke Verlag, Stuttgart, 1981.
The concentration of the acid in the solution should be more than 80 wt %, based on the total weight of cyanometallate complexes, preferably more than 90 wt % and more preferably more than 95 wt %.
The ligands containing heteroatoms used are the organic substances described above.
The concentration of the ligands in the suspension should be from 1 to 60 wt %, preferably from 5 to 40 wt % and more preferably from 10 to 30 wt %.
The multimetal cyanides used for execution of the process of the invention can be crystalline or amorphous. By crystalline multimetal cyanides we mean multimetal cyanides whose strongest reflex in the X-ray diffraction pattern has an intensity which is at least three times greater than the background reading. Crystalline multimetal cyanides can be cubic or show X-ray diffraction patterns such as are described in EP-A 755,715. By amorphous multimetal cyanides we mean those multimetal cyanides whose strongest reflex in the X-ray diffraction pattern has an intensity which is less than three times the intensity of the background or which show X-ray diffraction patterns such as are described in EP-A 654,302 and EP-A 743,093.
The multimetal cyanide compounds can be used for the synthesis of the polyether polyols of the invention either in powder form or in the form of shaped particles made by applying them to, or incorporating them in, macroscopic inorganic or organic support materials or shaping them to macroscopic shaped particles.
The aforementioned multimetal cyanide compounds are highly suitable for use in the process of the invention by reason of their high activity. The catalyst is preferably used in a concentration of less than 1 wt %, preferably less than 0.5 wt %, more preferably less than 1000 ppm and most preferably xe2x89xa6500 ppm, based on the total weight of the polyether polyol.
The process of the invention may be carried out continuously or batchwise. Synthesis can be carried out in suspension, in a fixed bed or in a fluidized bed. The temperatures during synthesis are between 50xc2x0 and 200xc2x0 C., temperatures between 90xc2x0 and 150xc2x0 C. being preferred.
The alkylene oxide that is used can be selected from the group comprising ethylene oxide, propylene oxide, butylene oxide, vinyl oxirane or mixtures thereof, ethylene oxide and propylene oxide being preferably used.
The polyether alcohols produced by the process of the invention preferably have molecular weights ranging from 2,000 to 10,000 g/mol. They are used, in particular, for reaction with isocyanates to form flexible polyurethane foams.
When using the batch starters of the invention the process of, preparing polyetherols with multimetal cyanide compounds shows very good starting characteristics and alkoxylation runs very reliably. By combining the batch starters used in the process of the invention with known batch starters or addition initiators of higher functionality, preferably trifunctional initiators, polyether polyols having functionalities of more than 2 become readily available. Of particularly great industrial significance are polyether polyalcohols used for flexible foams and having OH functionalities of from 2.1 to 2.6, as are industrially preferably used. The process of the invention considerably increases the number of possible applications of catalysis involving multimetal cyanide compounds.